Resize

The Resize transformation is used to make an image smaller or larger. This can be done in two fundamentally different ways:

Resample -- Resamples the image by altering its width and height in pixels. This method changes the image data and file size. For example, you may want to make reduce the size of an image so it can be emailed more easily or for use on the web. Resampling can either preserve the image proportions or it can alter the image proportions by applying different horizontal and vertical scale factors. This can be useful, for example, if you have an image you need to print as an 8 x 10, but it’s proportions are slightly off and you don’t want to crop it.

Don't Resample -- Changes the resolution of the image without resampling it. This method alters the physical size of the image without changing any of the pixels. While not affecting the underlying image, changing the physical size is mostly useful to indicate a preferred output size for printing or exporting to a word processor or page layout program.

Set

These controls determine whether you resample the image or not, and how you want to specify the new size. The Set control behaves differently depending on the Resample/Don’t Resample setting. Any options that do not apply are grayed out.

Set (Resample)

If Resample is selected, the output image size in pixels may be larger or smaller than the input image. When enlarging an image, new pixels are interpolated between existing pixels. When reducing an image, groups of pixels are combined into a single pixel to make the image smaller. There are many different resampling techniques which produce different results.

Pixel Width -- Set image width in pixels and resolution - image height is calculated to preserve the input image proportions.

Pixel Height -- Set image height in pixels and resolution - image width is calculated to preserve the input image proportions.

Pixel Width & Height -- Set width and height of image in pixels and resolution - use this to change the image proportions.

Physical Width -- Set width of image in physical units and resolution - image height is calculated to preserve proportions. The image width in pixels is computed by multiplying the physical width by the resolution.

Physical Height -- Set height of image in physical units and resolution - image width is calculated to preserve proportions. The image height in pixels is computed by multiplying the physical height by the resolution.

Physical Width & Height -- Set image width and height in physical units and resolution - use this if you want to change the image proportions.

Memory -- Set image size in megabytes (MB) while preserving proportions. The actual value may differ slightly since image width and height are integers.

Pixel Short Side -- Set the image shorter side in pixels and resolution - image longer side is calculated to preserve the input image proportions.

Pixel Long Side --  Set the image longer side in pixels and resolution - image shorter side is calculated to preserve the input image proportions.

Physical Short Side -- Set image shorter side in physical units and resolution - image longer side is calculated to the input image preserve proportions. The image dimension in pixels is computed by multiplying the physical dimension by the resolution.

Physical Long Side -- Set image longer side in physical units and resolution - image shorter side is calculated to the input image preserve proportions. The image dimension in pixels is computed by multiplying the physical dimension by the resolution.

Pixel Bounding Rectangle -- Makes the image as large as possible while still fitting inside a given width and height in pixels.

Physical Bounding Rectangle -- Makes the image as large as possible while still fitting inside a given width and height in physical units.

Pixel Percentage -- Multiplies the current size in pixels by a percentage, while preserving the input image proportions, where 100% mean leave it unchanged.

Physical Percentage -- Multiplies the current size in physical units by a percentage, while preserving the input image proportions, where 100% mean leave it unchanged.

Set (Don’t Resample)

If Don't Resample is selected, the output image is simply a copy of the input image, with its resolution (dpi) setting changed. This alters the physical size of the image without modifying any of the pixels.

Physical Width -- Set width of image in physical units. The resolution is computed by dividing the width in pixels by the physical width.

Physical Height -- Set height of image in physical units. The resolution is computed by dividing the height in pixels by the physical height.

Resolution -- Set image resolution.

Physical Short Side -- Set image shorter side in physical units. The resolution is computed by dividing the dimension in pixels by the physical dimension.

Physical Long Side -- Set image longer side in physical units. The resolution is computed by dividing the dimension in pixels by the physical dimension.

Physical Bounding Rectangle -- Makes the image as large as possible while still fitting inside a given width and height in physical units.

Physical Percentage -- Multiplies the current size in physical units by a percentage, where 100% mean leave it unchanged.

Depending on the current resolution setting, if you enter physical units they may come back slightly off since image dimensions in pixels must be integers.

Units

You can set the physical units to in, cm, or mm. You can set the resolution units to dpi, dpcm, or dpmm.

Readouts

The readouts below the separator line display the width and height in pixels, the physical width and height in units you can select (in/cm/mm), the resolution in the current resolution units (dpi/dpcm/dpmm), the file size in MB and the proportions – both before and after resizing. The values are updated automatically when you change the settings above the separator line.

Resampling

If Resample is selected, this is where you select a resampling method. Except for Nearest Neighbor, the differences between the methods are mostly very subtle.

Nearest Neighbor -- This setting selects the simplest method of resampling, called nearest neighbor. The color of each pixel in the output image is the color of the nearest pixel in the input image. This interpolation method is extremely fast, but when making an image larger, the individual pixels become visible as little blocks of solid color and when making an image smaller the effect can be coarse with jagged edges.

An interesting effect can be obtained by resizing an image smaller using Bicubic interpolation and then larger again using Nearest Neighbor. This converts the image to a sort of mosaic made up of large blocky pixels.

Bilinear -- Bilinear interpolation uses only the four neighboring pixels. It produces slightly softer results than the default Bicubic method.

Bicubic -- This is the default setting and produces high quality results. When resizing the input image, new pixels are computed by interpolating between the existing pixels using bicubic resampling. When this method is selected an additional sharpening slider is available. The default setting of 16.7% is recommended; moving the slider alters the bicubic convolution kernel to add or remove a little sharpening during the resampling process -- this makes only a very subtle difference.

Lanczos -- These settings use a method called Lanczos-windowed sinc resampling to resize the input image. The larger the window, the larger the neighborhood of pixels used to interpolate between pixels. Using more pixels means you can obtain slightly more accurate resampling at the expense of increased computation times. These higher quality resampling methods may be useful when you need to scale an image by 200% or more and want to squeeze out the most resolution possible. The Lanczos 4x4 method produces nearly identical results to Bicubic resampling; the Lanczos 6X6 and Lanczos 8X8 methods produces slightly better results.

Tips

You can enter size and resolution values either as number or as expressions such as 3.6/2+5. For example, say the current width is 1356 pixels, to decrease it by 15%, enter 1356*0.85 -- this multiplies the current width by 0.85. For more information on entering expressions, see General Tips.